Especially when machining crankpins for crankshafts on a grinding machine, during the machining process it is necessary to measure continuously whether a desired dimension has been attained and thus the machining process can be terminated or whether the machining process should be continued until the desired dimension has been attained. During in-process measuring, a measuring prism is used, for instance, the legs or edges of which are held in contact with the crankpin to be measured using a suitable mechanism. Using a measuring sensor that is arranged linearly movable on the measuring prism, measurement values are recorded that represent the shape of the crankpin. In the known method, the measurement values are recorded while the crankpin is rotating orbitally about a rotational axis that is parallel to the pin axis and the rotational axis of a grinding wheel being used. Because of the orbital rotation of the crankpin, during which rotation the measuring prism and measuring sensor are held in contact with the crankpin, the measuring prism and thus the measuring sensor rotate relative to the crankpin. If a certain number of measured values are recorded during one complete 360° rotation by the crankpin, these measured values are not allocated to equidistant points along the circumference of the crankpin due to the relative movement between the crankpin and the measuring sensor.
To prevent this from distorting the shape of the workpiece determined using the measured values it is necessary to take into account in the evaluation the relative rotation of the measuring sensor relative to the crankpin.
From EP 1 263 547 B1 a method is known for determining the shape of a workpiece in which measured values representing the shape of the workpiece are recorded and stored in the aforesaid manner by means of a measuring sensor, the workpiece in the method described in EP 1 263 547 B1 being a crankpin for a crankshaft. In the known method, the relative rotation between the measuring sensor and the crankpin is determined, and the measured values recorded by means of the measuring sensor are pre-processed for compensating the relative rotation. From EP 1 263 547 B1, and also from U.S. Pat. No. 5,077,908, EP 0 068 082 A2, and the publication, “Automated Three-Point Measurement for Determining Roundness on Piston Pins”, a research paper by Jörg Seewig, University of Hannover, Electrical Engineering Department, December 1992, it is known to subject the pre-processed measured values to a Fourier analysis (harmonic analysis) in order to calculate the shape of the workpiece from the measured values that were found by means of the measuring arrangement, which comprises the measuring prism and the measuring sensor.